Medical devices, particularly synthetic resin prosthetic devices which are used in environments where micro-organisms such as fungi or yeast and/or bacteria are actively growing, can become covered with a biofilm colonized layer to the point where the function of the device is impaired. After growth of the biofilm microbial layer, filaments can grow and descend into the body or wall of the polymeric device and detrimentally affect its physical properties until the device no longer functions. The fouled device must be cleaned or discarded.
Whenever a prosthesis is in contact with moisture in a warm, dark environment, the surfaces are subject to microbial growth, usually containing a predominant amount of Candida usually mixed with bacteria. The microbial growth can interfere with the functioning of the prosthesis, requiring removal of the prosthesis for disposal or cleaning. The microbial growth is a persistent problem in the management and care of patients who have had their larynx removed and utilize a voice prosthesis since the prosthesis is exposed to a non-sterile, humid, warm, nutrient rich environment.
There are several options for restoring speech to patients who have had their larynx removed. One procedure is to surgically create a puncture or fistula between the trachea and the esophagus. A tracheoesophageal voice prosthesis containing a one-way valve such as a BLOM-SINGER® voice prosthesis is inserted into the tracheoesophageal fistula. The one-way valve protects the airway during swallowing but opens under positive pressure from the trachea. The voice prosthesis, thus, permits a patient to divert air from the lungs into the esophagus and out through the mouth. Speech is created during passage of air through the upper part of the esophagus.
The prosthesis maintains the fistula open, transfers air from the trachea to the esophagus for voice production and prevents esophageal leakage into the trachea during swallowing. The oral cavity which extends into the throat has a high microbial population. However, the prosthesis being in contact with moisture in a warm, dark, nutrient rich environment is subject to growth of commonly found micro-organisms, typically Candida on the valve and the retaining flange. The microbial attack is currently being studied. The microbial attack organisms and sequence of events are quite complex and are still undetermined. The microbial growth on and into the soft silicone resin can interfere with function of the valve and can cause the flange to wrinkle and the valve to leak. The fouled device must be cleaned or discarded and replaced with a new device.
One type of current low pressure voice prosthesis can be removed by the patient every few days and can be replaced with a clean prosthesis. The removed prosthesis is soaked in hydrogen peroxide to sterilize and clean the valve and flange. Some patients however, have difficulty managing frequent removal and reinsertion of the prosthesis. Others, who are physically handicapped are not able to remove, sterilize, or reinsert the prosthesis.
A longer dwelling, low pressure voice prosthesis has been developed that can remain in place in the tracheoesophageal fistula for many weeks or months, depending on the patient and conditions of use. The patient can confidently use the prosthesis for longer periods. The longer dwelling voice prosthesis is not removable by the patient. Trips to a health care specialist to remove and replace the prosthesis are greatly extended providing increased comfort and lower cost to the patient.
Another type of soft voice prosthesis includes a rigid stiffening ring 14 inserted into a groove in the soft body of the prosthesis. Though the ring stiffens the body adjacent the valve it does not prevent distortion of the body by muscular movement or distortion of the valve by growth of yeast.
U.S. Pat. No. 5,578,083 issued Nov. 26, 1996, discloses the use of a stiff cartridge to support the soft silicone prosthesis and to provide a seat for the valve which is connected to the cartridge by a tab in slot design. Another cartridge-valve design includes a one piece sleeve-valve which is stretched over and seats in a cylindrical groove in the cartridge as disclosed in U.S. Ser. No. 10/487,614, filed Feb. 19, 2004, the disclosure (051) of which is incorporated herein by reference. However, microbial growth can still proceed to a point at which the valves can not be reliably sealed.
Microbial growth on the valve can also cause distortion of the shape of the valve or form wrinkles in the body of the valve which prevents the valve from closing. Leaking also appears to be due to distortion of the valve body adjacent to the seat of the valve and to microbial growth on the seat. Forming the valve with an arcuate dome shape increased resistance to folding or bending of the valve. However, some valves still leaked after extended placement in a fistula.
The use of silicone elastomer is limiting because of the open matrix nature of the material. The open nature of silicone allows microorganisms to attach to and sometimes burrow through the material. The attachment of microorganisms at the valve seat interface can interfere with creating a seal. Attachment of microorganisms to the flexible hinge area can reduce the flexibility of the hinge, and can also be a precursor for other microorganisms to burrow into the silicone, effectively changing the shape of the silicone and thereby interfering with the ability for the valve to seal correctly. In extreme cases, microorganisms can attach and burrow into the esophageal side of the valve to the point where the sealing seat of the valve is altered in shape.
Historically, microbial ingrowth resistance has come from selection of hard plastics and metals that reduce attachment of microorganisms to certain components. These materials were restricted from use in the hinge area and other areas that required flexibility and resilience. The components requiring this flexibility and resilience have traditionally been molded from silicone elastomer.
In other medical devices, antimicrobial coatings have been available for some years. Coatings typically do not last the lifetime of the product on the highly flexible hinge, as the coating tends to flake off. Once this happens, the hinge is left unprotected and is exposed to the effects of microorganisms.
Application of antimicrobial substances to silicone articles can also come by way of solvent introduction. In this method, the silicone part is soaked with a solvent containing a dissolved antimicrobial agent. The silicone part is removed from the solvent and the solvent is allowed to evaporate. The dissolved antimicrobial agent is then deposited in the matrix of the silicone elastomer. There are several variations of this method. This method is limited to antimicrobial agents that are soluble in an effective solvent and to the uncertainty of exact load level. This method also requires the additional steps and regulations associated with working with solvents.
The use of polymers having antimicrobial properties is disclosed in PCT Publication No. WO98/04463 published March 1998. Through the voice prosthesis device formed of flurosilicone polymer showed same initial success, examination of returned devices from a clinical study showed significant microbial growth on both the posterior aspect and periphery of the valve flap and on the inner surface of the valve hood which interfered with movement of the valve flap. Any further use of the flurosilicone device was abandoned.
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